I've always found the whole skull motif on undead armies a bit stupid. I would think that if someone were to become a necromancer they probably wouldn't care much about what they were wearing and they really wouldn't care what their soldiers were wearing.
I can't imagine they would be animating 20 skeleton blacksmiths to pound out skull bosses for shields or the like.
It just makes sense to me that the undead armies would fight wearing whatever it was they were buried in and fight with whatever weapons they could get their hands on. Also it never really made sense that they would be armoured as you would remove most armour before you buried someone, unless they were from some pile of dead warriors in some cataclysmic battle that was in a remote place and no one survived.
Or your necromancer is hanging around all kinds of dodgy places waiting for people to be killed by nature.
So the bright colours on necromancers work for me. They just picked up whatever cloth was at hand to wear, or not wear as is the case with your pair. Or pair of pairs.